bsd-comp.c

经典的ppp程序

{
    int i;

    if (opt_len < CILEN_BSD_COMPRESS
	|| options[0] != CI_BSD_COMPRESS || options[1] != CILEN_BSD_COMPRESS
	|| BSD_VERSION(options[2]) != BSD_CURRENT_VERSION
	|| BSD_NBITS(options[2]) != db->maxbits
	|| decomp && db->lens == NULL)
	return 0;

    if (decomp) {
	i = LAST+1;
	while (i != 0)
	    db->lens[--i] = 1;
    }
    i = db->hsize;
    while (i != 0) {
	db->dict[--i].codem1 = BADCODEM1;
	db->dict[i].cptr = 0;
    }

    db->unit = unit;
    db->hdrlen = hdrlen;
    db->mru = mru;
    if (debug)
	db->debug = 1;

    bsd_reset(db);

    return 1;
}

static int
bsd_decomp_init(state, options, opt_len, unit, hdrlen, mru, debug)
    void *state;
    u_char *options;
    int opt_len, unit, hdrlen, mru, debug;
{
    return bsd_init((struct bsd_db *) state, options, opt_len,
		    unit, hdrlen, mru, debug, 1);
}


/*
 * Update the "BSD Compress" dictionary on the receiver for
 * incompressible data by pretending to compress the incoming data.
 */
static void
bsd_incomp(state, dmsg, mlen)
    void *state;
    u_char *dmsg;
    int mlen;
{
    struct bsd_db *db = (struct bsd_db *) state;
    u_int hshift = db->hshift;
    u_int max_ent = db->max_ent;
    u_int n_bits = db->n_bits;
    struct bsd_dict *dictp;
    u_int32_t fcode;
    u_char c;
    long hval, disp;
    int slen, ilen;
    u_int bitno = 7;
    u_char *rptr;
    u_int ent;

    rptr = dmsg;
    ent = rptr[0];		/* get the protocol */
    if (ent == 0) {
	++rptr;
	--mlen;
	ent = rptr[0];
    }
    if ((ent & 1) == 0 || ent < 0x21 || ent > 0xf9)
	return;

    db->seqno++;
    ilen = 1;		/* count the protocol as 1 byte */
    ++rptr;
    slen = dmsg + mlen - rptr;
    ilen += slen;
    for (; slen > 0; --slen) {
	c = *rptr++;
	fcode = BSD_KEY(ent, c);
	hval = BSD_HASH(ent, c, hshift);
	dictp = &db->dict[hval];

	/* validate and then check the entry */
	if (dictp->codem1 >= max_ent)
	    goto nomatch;
	if (dictp->f.fcode == fcode) {
	    ent = dictp->codem1+1;
	    continue;   /* found (prefix,suffix) */
	}

	/* continue probing until a match or invalid entry */
	disp = (hval == 0) ? 1 : hval;
	do {
	    hval += disp;
	    if (hval >= db->hsize)
		hval -= db->hsize;
	    dictp = &db->dict[hval];
	    if (dictp->codem1 >= max_ent)
		goto nomatch;
	} while (dictp->f.fcode != fcode);
	ent = dictp->codem1+1;
	continue;	/* finally found (prefix,suffix) */

    nomatch:		/* output (count) the prefix */
	bitno += n_bits;

	/* code -> hashtable */
	if (max_ent < db->maxmaxcode) {
	    struct bsd_dict *dictp2;
	    /* expand code size if needed */
	    if (max_ent >= MAXCODE(n_bits))
		db->n_bits = ++n_bits;

	    /* Invalidate previous hash table entry
	     * assigned this code, and then take it over.
	     */
	    dictp2 = &db->dict[max_ent+1];
	    if (db->dict[dictp2->cptr].codem1 == max_ent)
		db->dict[dictp2->cptr].codem1 = BADCODEM1;
	    dictp2->cptr = hval;
	    dictp->codem1 = max_ent;
	    dictp->f.fcode = fcode;

	    db->max_ent = ++max_ent;
	    db->lens[max_ent] = db->lens[ent]+1;
	}
	ent = c;
    }
    bitno += n_bits;		/* output (count) the last code */
    db->bytes_out += bitno/8;
    db->in_count += ilen;
    (void)bsd_check(db);

    ++db->incomp_count;
    db->incomp_bytes += ilen;
    ++db->uncomp_count;
    db->uncomp_bytes += ilen;

    /* Increase code size if we would have without the packet
     * boundary and as the decompressor will.
     */
    if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode)
	db->n_bits++;
}


/*
 * Decompress "BSD Compress"
 *
 * Because of patent problems, we return DECOMP_ERROR for errors
 * found by inspecting the input data and for system problems, but
 * DECOMP_FATALERROR for any errors which could possibly be said to
 * be being detected "after" decompression.  For DECOMP_ERROR,
 * we can issue a CCP reset-request; for DECOMP_FATALERROR, we may be
 * infringing a patent of Motorola's if we do, so we take CCP down
 * instead.
 *
 * Given that the frame has the correct sequence number and a good FCS,
 * errors such as invalid codes in the input most likely indicate a
 * bug, so we return DECOMP_FATALERROR for them in order to turn off
 * compression, even though they are detected by inspecting the input.
 */
static int
bsd_decompress(state, cmsg, inlen, dmp, outlenp)
    void *state;
    u_char *cmsg, *dmp;
    int inlen, *outlenp;
{
    struct bsd_db *db = (struct bsd_db *) state;
    u_int max_ent = db->max_ent;
    u_int32_t accm = 0;
    u_int bitno = 32;		/* 1st valid bit in accm */
    u_int n_bits = db->n_bits;
    u_int tgtbitno = 32-n_bits;	/* bitno when we have a code */
    struct bsd_dict *dictp;
    int explen, i, seq, len;
    u_int incode, oldcode, finchar;
    u_char *p, *rptr, *wptr;
    int ilen;
    int dlen, space, codelen, extra;

    rptr = cmsg;
    if (*rptr == 0)
	++rptr;
    ++rptr;			/* skip protocol (assumed 0xfd) */
    seq = (rptr[0] << 8) + rptr[1];
    rptr += BSD_OVHD;
    ilen = len = cmsg + inlen - rptr;

    /*
     * Check the sequence number and give up if it is not what we expect.
     */
    if (seq != db->seqno++) {
	if (db->debug)
	    printf("bsd_decomp%d: bad sequence # %d, expected %d\n",
		   db->unit, seq, db->seqno - 1);
	return DECOMP_ERROR;
    }

    wptr = dmp + db->hdrlen;

    oldcode = CLEAR;
    explen = 0;
    while (len > 0) {
	/*
	 * Accumulate bytes until we have a complete code.
	 * Then get the next code, relying on the 32-bit,
	 * unsigned accm to mask the result.
	 */
	bitno -= 8;
	accm |= *rptr++ << bitno;
	--len;
	if (tgtbitno < bitno)
	    continue;
	incode = accm >> tgtbitno;
	accm <<= n_bits;
	bitno += n_bits;

	if (incode == CLEAR) {
	    /*
	     * The dictionary must only be cleared at
	     * the end of a packet.  But there could be an
	     * empty message block at the end.
	     */
	    if (len > 0) {
		if (db->debug)
		    printf("bsd_decomp%d: bad CLEAR\n", db->unit);
		return DECOMP_FATALERROR;
	    }
	    bsd_clear(db);
	    explen = ilen = 0;
	    break;
	}

	if (incode > max_ent + 2 || incode > db->maxmaxcode
	    || incode > max_ent && oldcode == CLEAR) {
	    if (db->debug) {
		printf("bsd_decomp%d: bad code 0x%x oldcode=0x%x ",
		       db->unit, incode, oldcode);
		printf("max_ent=0x%x dlen=%d seqno=%d\n",
		       max_ent, dlen, db->seqno);
	    }
	    return DECOMP_FATALERROR;	/* probably a bug */
	}

	/* Special case for KwKwK string. */
	if (incode > max_ent) {
	    finchar = oldcode;
	    extra = 1;
	} else {
	    finchar = incode;
	    extra = 0;
	}

	codelen = db->lens[finchar];
	explen += codelen + extra;
	if (explen > db->mru + 1) {
	    if (db->debug)
		printf("bsd_decomp%d: ran out of mru\n", db->unit);
	    return DECOMP_FATALERROR;
	}

	/*
	 * Decode this code and install it in the decompressed buffer.
	 */
	p = (wptr += codelen);
	while (finchar > LAST) {
	    dictp = &db->dict[db->dict[finchar].cptr];
#ifdef DEBUG
	    --codelen;
	    if (codelen <= 0) {
		printf("bsd_decomp%d: fell off end of chain ", db->unit);
		printf("0x%x at 0x%x by 0x%x, max_ent=0x%x\n",
		       incode, finchar, db->dict[finchar].cptr, max_ent);
		return DECOMP_FATALERROR;
	    }
	    if (dictp->codem1 != finchar-1) {
		printf("bsd_decomp%d: bad code chain 0x%x finchar=0x%x ",
		       db->unit, incode, finchar);
		printf("oldcode=0x%x cptr=0x%x codem1=0x%x\n", oldcode,
		       db->dict[finchar].cptr, dictp->codem1);
		return DECOMP_FATALERROR;
	    }
#endif
	    *--p = dictp->f.hs.suffix;
	    finchar = dictp->f.hs.prefix;
	}
	*--p = finchar;

#ifdef DEBUG
	if (--codelen != 0)
	    printf("bsd_decomp%d: short by %d after code 0x%x, max_ent=0x%x\n",
		   db->unit, codelen, incode, max_ent);
#endif

	if (extra)		/* the KwKwK case again */
	    *wptr++ = finchar;

	/*
	 * If not first code in a packet, and
	 * if not out of code space, then allocate a new code.
	 *
	 * Keep the hash table correct so it can be used
	 * with uncompressed packets.
	 */
	if (oldcode != CLEAR && max_ent < db->maxmaxcode) {
	    struct bsd_dict *dictp2;
	    u_int32_t fcode;
	    int hval, disp;

	    fcode = BSD_KEY(oldcode,finchar);
	    hval = BSD_HASH(oldcode,finchar,db->hshift);
	    dictp = &db->dict[hval];

	    /* look for a free hash table entry */
	    if (dictp->codem1 < max_ent) {
		disp = (hval == 0) ? 1 : hval;
		do {
		    hval += disp;
		    if (hval >= db->hsize)
			hval -= db->hsize;
		    dictp = &db->dict[hval];
		} while (dictp->codem1 < max_ent);
	    }

	    /*
	     * Invalidate previous hash table entry
	     * assigned this code, and then take it over
	     */
	    dictp2 = &db->dict[max_ent+1];
	    if (db->dict[dictp2->cptr].codem1 == max_ent) {
		db->dict[dictp2->cptr].codem1 = BADCODEM1;
	    }
	    dictp2->cptr = hval;
	    dictp->codem1 = max_ent;
	    dictp->f.fcode = fcode;

	    db->max_ent = ++max_ent;
	    db->lens[max_ent] = db->lens[oldcode]+1;

	    /* Expand code size if needed. */
	    if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode) {
		db->n_bits = ++n_bits;
		tgtbitno = 32-n_bits;
	    }
	}
	oldcode = incode;
    }
    *outlenp = wptr - (dmp + db->hdrlen);

    /*
     * Keep the checkpoint right so that incompressible packets
     * clear the dictionary at the right times.
     */
    db->bytes_out += ilen;
    db->in_count += explen;
    if (bsd_check(db) && db->debug) {
	printf("bsd_decomp%d: peer should have cleared dictionary\n",
	       db->unit);
    }

    ++db->comp_count;
    db->comp_bytes += ilen + BSD_OVHD;
    ++db->uncomp_count;
    db->uncomp_bytes += explen;

    return DECOMP_OK;
}
#endif /* DO_BSD_COMPRESS */